The present invention concerns tools for borehole applications, in particular oil wells, gas wells or water-wells, more particularly including installations for primary, secondary or tertiary oil production, whether holes for injecting water, gas or another pressurizing agent (injector holes) or oil extraction (production wells). A particular application of the tool is in injector and producer multi-zone wells where the number of isolation zones is high and/or the wellbore casing is damaged or diverted, to quickly and economically isolate areas with damaged casing.
The present invention applies to tools carrying a packer device comprising seals mounted to a mandrel and forming with other operational components a tubing string (or just “tubing”) of tools and components joined one after another for lowering down a multifunctional (or multizonal) well, i.e. having multiple layers or strata which should be isolated from one another. Packer tools are not unusual in the oil industry. The tubing string comprising a number of function-specific tools is lowered into a well, maintaining an annular space between the tubing string and a well casing.
Packer tools generally comprise two basic elements: packer seals for isolating annular regions thereabove and below and anchor slips to affix the tool to a point of the casing. A packer sealing element is a ring made of metal and typically dense synthetic rubber that fits around the tubing in a well. The packer seal (the “packing element”) of a packer tool (the “packer”) is typically a rubber ring that expands against the side of the casing lining the side of the wellbore. A packer may, and usually will, have more than one packing element. In the majority of active wells in the world today, this tubing is used to either produce oil or gas out of the well and serve as a conduit to transport water into the well for water injection and water flood applications. The packer provides a secure packer seal between everything above and below where it is set. The main reasons for using a packer are to keep sediment, sand and other potentially corrosive or erosive materials from flowing into the annulus and damaging the casing, and to control the zone of the well from which hydrocarbons are being produced in a producer well or to control the zone where water is being injected in an injection well.
Slips hold the packer in place and prevent them from moving once they are set in the well. A slip is a serrated piece of metal that grips the side of the casing. Some packers lack a specific anchor device (in which case they are known as packer-tandems).
Insofar as the present invention is concerned, the packer tool sequentially carries out the following phases:
Run-in: The tubing enters the well and the packer is lowered down to a set position.
Setting: Both the anchor slips and the packer seals are pushed outwards to respectively clamp the tool to the well while the tubing is down the well, isolating annular regions above and below the packer. The tool setting system may be mechanical, involving rotation or axial compression or traction, or else hydraulic by injecting a pressurizing fluid.
Release: This operation is carried out on removable tools to unset them from the well casing in order that they may be extracted. In tools having release systems, known as removable packers, release may be based on similar maneuvers or a combination thereof. Tools lacking a release system are known as permanent packers which need to be rotated to literally destroy the tool by machine milling. This operation is costly and time-consuming.
Extraction: The removable packer is hauled up to the mouth of the well.
The invention particularly relates to a packer tool that is removable, hydraulically set and mechanically released.
The present invention concerns packer tools—whether of the tandem type or not (i.e. without or with anchor devices), in particularly regarding safety features thereof for preventing accidental operations during the run-in, dwelling time and extraction from the well. More particularly, they refer to the sequence and time-frames involved in different operational movements which involve the packer seals—as well as the anchor means if present—to convey reliability to the tool operation, avoid undue movements causing the sequence to untimely jump ahead or go back at any time.
Use of mechanically- or hydraulically-actuated packer tools or, simply, packers for maintaining separation between production layers or fluid injection layers is well known in the oil industry.
The best known release systems are by rotation and traction. In the first system, the tool is released by rotating it several turns, which complicates the operation the deeper in the well because of the greater number of tools. This in turn makes the operation unreliable through uncertainty regarding which tool is actually being operated.
In traction release, tractive tension is applied to the piping to shear a number of brass or steel pins. Once set, this kind of tool is subject to stress from temperature and pressure variations down the well, which get worse with increased depth to the point that pins may shear producing accidental tool release.
U.S. Pat. No. 4,319,639 (Mott) and U.S. Pat. No. 4,832,129 (Sproul et al) are examples of the use of shear pins to prevent undue setting and release of the tool. The problem with shear pins is, precisely, that they are designed to fail when subjected to calculated shear forces. Sufficient shear forces may arise in unforeseen circumstances such a from jarring during run-in and downhole temperature-induced tool-length expansion and pressure surges.
In some operations, in which the tool has to be moved upwards for some reason, the setting anti-shear pins may fail leading to accidental tool setting. This may occur when for some reason (coupling, paraffin, casing failure, etc.) the packer or the packing mechanism receives a longitudinal up-to-down force, generally applied to the greater tool diameter, i.e. one of the calibrator rings, and transmitted to the setting shear pins which break off thereby undesirably setting the tool.
U.S. Pat. No. 4,834,175 (Ross & White) discloses a well packer with annular packing seals and anchor slips with a hydraulic setting actuator in between. The actuator includes a piston for setting the slips and a cylinder for setting the seal elements. A snap ring prevents the piston and cylinder from moving away from each other while they are mechanically interlocked thus preventing premature setting of the tool.
Some prior art packers have a split-mandrel system having several drawbacks. One such drawback is pasting of the screw-threads joining two mandrels thereby causing difficulties in tool release. Moreover, the release mechanism in split-mandrel systems tend to be unreliable. Another drawback thereof is dead time during the release operation during which the tool turns freely and are uselessly unable to transmit torque down to other tools in the tubing.
When connecting the packing device between upper and lower tubings at the mouth of the well, it is necessary to adjust them by turning the joints of the subs with the tubings in opposite directions, that is to carry out a counterscrew. Some packer tools may suffer a sudden accidental “release” when carrying out this maneuver and may not operate any further. Moreover, if the sudden “release” happens before setting, the tool may not be set later and operation is hampered thereafter.
Stresses caused by pressure and temperature variations as a result of changes and movements of flow control valves may affect the packer release mechanisms operating with pins, accidentally releasing some tools and hindering operation thereafter.
U.S. Pat. No. 5,141,053 (Restarik & White) discloses a packer with expandable seal and slip anchoring assemblies. Each anchor slip includes curved upper and lower gripping surfaces positioned to radially expand through cage windows. Radially retractile locking dogs prevent premature tool setting and release. The fact that the dogs are in an extended position protruding from the tool surface during tool run-in and extraction may hinder transit down and up a borehole.